Replace realtime

[chatch]

Supabase realtime will not work with self hosted on timescale cloud because:

• logic replication is not available
• parameters can not be set (although a fork of realtime could remove parameters setting from the migration)

What are we currently using realtime for:

• subscribe to updates to myenergy.contracts - updates app state - contract signed status
• subscribe to updates to myenergy.customers - updates app state - customer status and flags

Potential replacement:

• setup websockets with Spring in the accounts service (see STOMP)
• trigger on tables sends NOTIFY on row update
• setup a new NOTIFY/LISTEN channel in the accounts service
• setup a new listener that will construct a STOMP message
• use a STOMP client in the flutter app to subscribe to messages